Immunoassay and antibodies for the detection of chromogranin a

ABSTRACT

The present invention relates to an immunoassay method for the detection of Chromogranin A (or fragment(s) thereof) comprising the steps of contacting a sample suspected of comprising Chromogranin A with a first antibody or an antigen-binding fragment or derivative thereof specific for Chromogranin A and a second antibody or an antigen-binding fragment or derivative thereof specific for Chromogranin A under conditions allowing for the formation of a ternary complex between Chromogranin A and the two antibodies or antigen-binding fragments or derivates thereof, and detecting the binding of the two antibodies or antigen-binding fragments or derivates thereof to Chromogranin A. Also provided are antibodies directed against amino acid residues 124 to 144 and 280 to 301 of Chromogranin A and their use in the immunoassay method.

BACKGROUND OF THE INVENTION

Chromogranin A (CgA) is a protein that was identified and isolated in 1965 from chromaffin cells of bovine adrenal medulla (Banks et al. 1965. Biochem J 97: 40C-1C; Taupenot et al. 2010. New Eng J Med. 348: 1134-49). Chromaffin cells are neuroendocrine cells found mostly in the medulla of the adrenal glands in mammals. Chromogranin A is an established tumor marker in a variety of neuroendocrine tumors, a heterogeneous group of rare neoplasms from neuroendocrine cells comprising multiple endocrine neoplasia, type 1 and type 2 (MEN1/MEN2), medullary thyroid carcinoma, carcinoid tumors, islet cell tumors, pheochromocytoma/paraganglioma, poorly differentiated/small cell/atypical lung carcinoid, small cell carcinoma of the lung, Merkel cell carcinoma (Deftos et al. 1991. Endocr. Rev. 12: 181-7; Corti et al. 1996. Br J Cancer 73: 924-32) and mentioned in several guidelines (Ramage et al. 2012. Gut 61: 6-32; Vinik et al. 2010. NANETS Pancreas 39(6): 713-734; Pape et al. 2012. ENETS 95: 135-156).

Human Chromogranin A has a sequence of 439 amino acid residues (see SEQ ID NO:1) constituting a 49 kDa acidic glycoprotein that is stored and released from the chromaffin granules of endocrine cells, neurons and neurendocrines cells along with their respective hormones, neurotransmitters, and neuropeptides (Kim et al. 2001. Cell 106: 499-509).

Chromogranin A is the main member of the chromogranin/secretogranin family which consists of a group of proteins derived from different genes but share a number of characteristics, namely an abundance of acidic amino acid residues and numerous pairs of basic amino acids as potential positions for post-translational processing (Metz-Boutigue et al. 1993. Eur. J. Biochem 217: 247-257) and cleavage.

CgA is the precursor of several biologically active peptide fragments that have been described in human and in other species: vasostatins (Drees et al. 1991. Endocrinology 129: 3381-7), chromostatin (Galindo et al. 1991. Proc Natl Acad Sci USA 88: 1426-30), chromacins (Strub et al. 1997. J Biol Chem 272: 11928-36), pancreastatin (Tatemoto et al. 1986. Nature 324: 476-8), WE-14 (Curry et al. 1992. FEBS Lett 301: 319-321), catestatin (Mahata et al. 1997. J Clin Invest 100: 1623-33), parastatin (Fasciotto et al. 1993. Endocrinology 133: 461-6) and GE-25 (Kirchmair et al. 1995. Biochem J 310 (Pt 1): 331-6). In the UniProt database, additional peptides for human Chromogranin A (accession number: P 10645) are mentioned, based on the cleavage sites that can predict the peptides to be released: vasostatin-1 comprises amino acid sequence 1-76, vasostatin-2 comprises amino acid sequence 1-113, EA-92 comprises amino acid sequence 116-207, ES-43 comprises amino acid sequence 210-242, pancreastatin comprises amino acid sequence 254-301, SS-18 comprises amino acid sequence 304-321, WE-14 comprises amino acid sequence 324-337, WA-8 comprises amino acid sequence 324-331, LF-19 comprises amino acid sequence 340-358, AL-11 comprises amino acid sequence 362-372, GV-19 comprises amino acid sequence 375-393, GR-44 comprises amino acid sequence 395-438 and ER-37 comprises amino acid sequence 402-438. Moreover, it has been shown that different neurendocrine cells can process the molecule differently (Portela-Gomes et al. 2001. J Histochem Cytochem 4: 483-90).

Chromgranin A has been described as a biomarker for a number of diseases and conditions including cancer, for example prostate cancer (WO 2013/070088 A1; WO 2013/070089 A1; U.S. Pat. No. 6,238,877 B1; WO 2012/065025 A2).

Today, four non radiative CE-marked commercial assays for the detection of Chromogranin A are available: The Cis-Bio ELISA assay (Cisbio Bioassays, Codolet, France) uses two monoclonal antibodies directed against epitopes corresponding to amino acids 145-197 and 219-234, the DAKO ELISA assay (Dako Denmark A/S, Glostrup, Denmark) uses rabbit polyclonal antibodies directed against a 23 kDa C-terminal fragment, the Euro-Diagnostica NEOLISA™ sandwich ELISA assay (Euro Diagnostica AB, Malmö, Sweden) uses two monoclonal antibodies directed against epitopes corresponding to amino acids 236-251 and 264-279 (also see WO 2011/135035 A1 and WO 99/58980 A1).

The only available fully automated assay for the detection of Chromogranin A is the Chromogranin A KRYPTOR assay (Thermo Fisher Scientific B.R.A.H.M.S GmbH, Hennigsdorf, Germany) which uses two monoclonal antibodies, one monoclonal antibody binding to an epitope corresponding to amino acids 250-301 (Popovici et al. 2014. Clin Biochem 47: 87-91).

Due to high proteolysis of the molecule, the measured concentration in these assays can vary depending on the storage of the collected sample over the time and depending on the fragment being measured by the antibodies in the assay, thus an improved assay for Chromogranin A should address the most stable fragments of the molecule and be assessed in terms of sample stability under different storage conditions.

Different publications describe the impact of antibody epitopes and assay design on clinical performance of Chromogranin A immunoassays (Corti et al. 1996. Eur J. Biochem 235: 275-280, Stridsberg et al. 2003. J Endocrinol 177: 337-41).

SUMMARY OF THE INVENTION

The present invention relates to a new assay design for the detection of Chromogranin A or fragments thereof. This assay uses one or more antibodies that bind to epitopes, which were previously characterized as poor or non-binding antigenic sites (Corti et al. 1996. Eur J. Biochem 235: 275-280). The assay of the present invention surprisingly shows an improved analyte stability in the sample compared to the existing fully automated Chromogranin A KRYPTOR assay (B.R.A.H.M.S GmbH, Hennigsdorf, Germany). The immunoassay provided herein further has a broad detection range, i.e. detection of the target protein is possible at least in a concentration range from about 9 ng/ml to about 3 mg/ml. The broad detection range leads to an economic advantage, because less samples need to be diluted. Hence, the assay of the present invention can, e.g., be used as a research tool and in clinical applications for the detection of Chromogranin A over a wide range of concentrations and with a high specificity. In terms of clinical applications, the assay of the present invention can be used for the detection of Chromogranin A in patients samples for diagnosis, prognosis, risk assessment, risk stratification, therapy-control and/or post-operative control of a disorder or medical condition.

In particular, the present invention provides an immunoassay method for the detection of Chromogranin A or a fragment thereof comprising the steps of:

-   -   a) contacting a sample suspected of comprising Chromogranin A         with a first antibody or an antigen-binding fragment or         derivative thereof specific for Chromogranin A and a second         antibody or an antigen-binding fragment or derivative thereof         specific for Chromogranin A under conditions allowing for the         formation of a ternary complex between Chromogranin A and the         two antibodies or antigen-binding fragments or derivates         thereof, and     -   b) detecting the binding of the two antibodies or         antigen-binding fragments or derivates thereof to Chromogranin         A.

In the immunoassay method according to the invention said first antibody may be specific for an epitope in the sequence of Chromogranin A (SEQ ID NO:1), preferably in the sequence spanning amino acids 124-144 of SEQ ID NO:1.

The immunoassay method of the invention can be used in the context of diagnostic methods. The invention further relates to antibodies and kits for the use in the methods of the invention.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a standard curve employing different concentrations of Chromogranin A using the immunoassay method of Example 4.

FIG. 2 shows the precision profile of an immunoassay of the present invention as compared to the prior art KRYPTOR Chromogranin A assay (Thermo Fisher Scientific B.R.A.H.M.S GmbH, Hennigsdorf, Germany) (Example 5).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an immunoassay method for the detection of Chromogranin A or fragments thereof. The immunoassay method is based on the detection of Chromogranin A using one or more antibodies, preferably monoclonal antibodies, that are specific for Chromogranin A. Preferably, the immunoassay detects epitopes in the sequence spanning amino acid residues 124 to 144 and/or 280 to 301 of the Chromogranin A sequence according to SEQ ID NO:1. Hence, fragments of Chromogranin A encompassing amino acid residues 124 to 144 and/or 280 to 301 of the Chromogranin A sequence can also be detected with the immunoassay provided herein. Herein, the terms “Chromogranin A or a fragment thereof” or “Chromogranin or fragment(s) thereof” therefore encompass Chromogranin A and all fragments thereof that comprise the epitope(s) detected by the immunoassay of the invention, i.e. that can be detected using the immunoassay of the invention. Preferably, the assay employs at least one antibody that detects an epitope in the sequence spanning amino acid residues 124 to 144 of the Chromogranin A sequence according to SEQ ID NO:1. Chromogranin A or—as the case may be—fragment(s) thereof can according to the immunoassay of the invention be qualitatively and/or quantitatively detected by the binding of one or preferably two antibodies to Chromogranin A or a fragment thereof. In the case of a sandwich immunoassay (i.e. employing two antibodies) the presence of Chromogranin A or its fragment will be detected if both antibodies bind the Chromogranin A or its fragment. In other words the invention in one embodiment relates to an immunoassay for the detection of Chromogranin A or a fragment thereof in a sample comprising the steps of contacting said sample with a first anti-Chromogranin A antibody (or an antigen-binding fragment or derivative thereof) and a second anti-Chromogranin A antibody (or an antigen-binding fragment or derivative thereof) and detecting the presence of ternary immune complexes of said antibodies and Chromogranin A (or fragment(s) thereof). The immune complexes will form under conditions that allow an immunoreaction between said antibody/antibodies and said sample (i.e. under conditions allowing for the binding of the antibody/antibodies to Chromogranin A or fragment(s) thereof, i.e. the formation of a ternary complex in case of a sandwich assay). In the immunoassay, preferably a combination of two antibodies may be used, e.g. in a sandwich format (see below). Hence, the present invention pertains to an immunoassay method for the detection of Chromogranin A (or a fragment thereof) comprising the steps of

-   -   a) contacting a sample suspected of comprising Chromogranin A         (or a fragment thereof) with a first antibody or an         antigen-binding fragment or derivative thereof specific for         Chromogranin A or a fragment thereof and a second antibody or an         antigen-binding fragment or derivative thereof specific for         Chromogranin A or a fragment thereof, and     -   b) detecting the binding of the two antibodies or         antigen-binding fragments or derivates thereof to Chromogranin A         or a fragment thereof. In the immunoassay method according to         the invention said first antibody is preferably specific for an         epitope in the sequence of Chromogranin A (SEQ ID NO:1),         preferably in the sequence spanning amino acids 124 to 144 of         SEQ ID NO:1. The first antibody is preferably a monoclonal         antibody.

The present invention also pertains to an immunoassay method for the detection of Chromogranin A (or a fragment thereof) comprising the steps of

-   -   a) contacting a sample suspected of comprising Chromogranin A         (or a fragment thereof) with a first antibody or an         antigen-binding fragment or derivative thereof specific for         Chromogranin A or a fragment thereof and a second antibody or an         antigen-binding fragment or derivative thereof specific for         Chromogranin A or a fragment thereof under conditions allowing         for the formation of a ternary complex between Chromogranin A or         a fragment thereof and the two antibodies or antigen-binding         fragments or derivates thereof, and     -   b) detecting the binding of the two antibodies or         antigen-binding fragments or derivates thereof to Chromogranin A         or a fragment thereof. In the immunoassay method according to         the invention said first antibody is preferably specific for an         epitope in the sequence of Chromogranin A (SEQ ID NO:1),         preferably in the sequence spanning amino acids 124 to 144 of         SEQ ID NO:1. The first antibody is preferably a monoclonal         antibody.

The invention also relates to an immunoassay method for the detection of Chromogranin A or fragments thereof comprising the steps of

-   -   a) contacting a sample suspected of comprising Chromogranin A         with an antibody or an antigen-binding fragment or derivative         thereof specific for Chromogranin A or a fragment thereof under         conditions allowing for the formation of an immune complex         between Chromogranin A and the antibody or antigen-binding         fragments or derivates thereof, wherein said first antibody is         specific for an epitope spanning amino acids 124 to 144 of the         Chromogranin A sequence (SEQ ID NO:1). The antibody being         specific for the epitope spanning amino acids 124 to 144 of the         Chromogranin A sequence is preferably the antibody produced by         hybridoma cell line 537/H2 deposited at the Leibniz-Institut         DSMZ-Deutsche Sammlung von Mikroorganismen and Zellkulturen GmbH         (DSMZ), Inhoffenstraβe 7B, 38124 Braunschweig, Germany, on Feb.         20, 2014 as DSM ACC3231.

In the following the term “antibody” also comprises antigen-binding fragments or derivatives unless otherwise stated.

The term “antibody” generally comprises monoclonal and polyclonal antibodies and binding fragments thereof, in particular Fc-fragments as well as so called “single-chain-antibodies” (Bird R. E. et al (1988) Science 242:423-6), chimeric, humanized, in particular CDR-grafted antibodies, and dia or tetrabodies (Holliger P. et al (1993) Proc. Natl. Acad. Sci. U.S.A. 90:6444-8). Also comprised are immunoglobulin-like proteins that are selected through techniques including, for example, phage display to specifically bind to the molecule of interest contained in a sample. In this context the terms “specific” and “specific binding” refer to antibodies raised against the molecule of interest or a fragment thereof. An antibody is considered to be specific, if its affinity towards the molecule of interest (here: Chromogranin A) or the aforementioned fragment thereof is at least 50-fold higher, preferably 100-fold higher, most preferably at least 1000-fold higher than towards other molecules comprised in a sample containing the molecule of interest. It is well known in the art how to develop and to select antibodies with a given specificity. As stated herein above, monoclonal antibodies are preferred.

As will be discussed herein below in more detail the (first and/or second) antibodies or antigen-binding fragments or derivatives thereof of the immunoassay method as described herein may for instance be polyclonal antibodies, monoclonal antibodies or genetically engineered monoclonal antibodies.

In the immunoassay method according to the invention said first antibody may be specific for an epitope in the sequence of Chromogranin A (SEQ ID NO:1), preferably in the sequence spanning amino acids 124 to 144 of SEQ ID NO:1. The first antibody is preferably a monoclonal antibody.

In the immunoassay method according to the invention said second antibody may be specific for an epitope in the sequence of Chromogranin A (SEQ ID NO:1), preferably in the sequence spanning amino acids 280 to 301 of SEQ ID NO: 1. The second antibody is preferably a monoclonal antibody.

In a particular embodiment of the immunoassay of the invention, the first antibody is specific for an epitope in the sequence of Chromogranin A (SEQ ID NO:1) spanning amino acid residues 124-144 and the second antibody is specific for an epitope in the sequence of Chromogranin A (SEQ ID NO:1) spanning amino acid residues 280 to 301. The first and second antibodies are preferably monoclonal antibodies.

The first antibody or antigen-binding fragment or derivative thereof may for example be produced by the hybridoma cell line 537/H2 deposited at the DSMZ (Inhoffenstraβe 7B, 38124 Braunschweig, Germany) on Feb. 20, 2014 as DSM ACC3231. The antibody produced by hybridoma cell line 537/H2 binds specifically to amino acid residues 124 to 144 of the Chromogranin A sequence (SEQ ID NO:1), i.e. to SEQ ID NO:2. It has been raised against the antigenic peptide of SEQ ID NO:4.

The second antibody or antigen-binding fragment or derivative thereof may for example be produced by the hybridoma cell line 541/E2 deposited at the DSMZ, Inhoffenstraβe 7B, 38124 Braunschweig, Germany, on Feb. 20, 2014 as DSM ACC3232. The antibody produced by hybridoma cell line 541/E2 binds specifically to amino acid residues 280 to 301 of the Chromogranin A sequence (SEQ ID NO:1), i.e. to SEQ ID NO:3. It has been raised against the antigenic peptide of SEQ ID NO:5.

In a particular embodiment of the immunoassay method of the invention, the first antibody is produced by the hybridoma cell line 537/H2 deposited at the DSMZ, Inhoffenstraβe 7B, 38124 Braunschweig, Germany, on Feb. 20, 2014 as DSM ACC3231 and the second antibody is produced by the hybridoma cell line 541/E2 deposited at the DSMZ, Inhoffenstraβe 7B, 38124 Braunschweig, Germany, on Feb. 20, 2014 as DSM ACC3232.

The binding of the antibodies to Chromogranin A (or a fragment thereof) takes place under suitable conditions (i.e. allowing for immunoreactions, i.e. binding of the antibodies to Chromogranin A and formation of immune complexes). Such conditions are known to the skilled person and standard formats of immunoassays e.g. as described below can be used. Such conditions will preferably be under physiologic temperature, pH and ionic strength and can take place in media such as, for example, phosphate buffered saline (PBS).

The preferred detection methods comprise immunoassays in various formats such as for instance radioimmunoassay (RIA), chemiluminescence- and fluorescence-immunoassays, enzyme immunoassay (EIA), Enzyme-linked immunoassays (ELISA), Luminex-based bead arrays, protein microarray assays, rapid test formats such as for instance immunochromatographic strip tests, and Selected/Multiple reaction monitoring (SRM/MRM).

The assays can be homogenous or heterogeneous assays, competitive and non-competitive assays. In a particularly preferred embodiment, the assay is in the form of a sandwich assay, which is a non-competitive immunoassay, wherein the molecule to be detected and/or quantified is bound to a first antibody and to a second antibody. The first antibody may be bound to a solid phase, e.g. a bead, a surface of a well or other container, a chip or a strip, and the second antibody is an antibody which is labeled, e.g. with a dye, with a radioisotope, or a reactive or catalytically active moiety or vice versa. The amount of labeled antibody bound to the analyte is then measured by an appropriate method. The general composition and procedures involved with “sandwich assays” are well-established and known to the skilled person (The Immunoassay Handbook, Ed. David Wild, Elsevier LTD, Oxford; 3rd ed. (May 2005), ISBN-13: 978-0080445267; Hultschig C et al., Curr Opin Chem Biol. 2006 February; 10(1): 4-10. PMID: 16376134, incorporated herein by reference).

In a particularly preferred embodiment, the assay comprises two antibodies which are both present as dispersions in a liquid reaction mixture, wherein a first labelling component is attached to the first antibody, wherein said first labelling component is part of a labelling system based on fluorescence- or chemiluminescence-quenching or amplification, and a second labelling component of said marking system is attached to the second antibody, so that upon binding of both capture molecules to the analyte a measurable signal is generated that allows for the detection of the formed sandwich complexes in the solution comprising the sample.

Even more preferred, said labelling system may comprise rare earth cryptates or rare earth chelates in combination with fluorescence dye or chemiluminescence dye, in particular a dye of the cyanine type.

In the context of the present invention, fluorescence based assays may comprise the use of dyes, which may for instance be selected from the group comprising FAM (5- or 6-carboxyfluorescein), VIC, NED, Fluorescein, Fluoresceinisothiocyanate (FITC), IRD-700/800, Cyanine dyes, such as CY3, CY5, CY3.5, CY5.5, Cy7, Xanthen, 6-Carboxy-2′,4′,7′,4,7-hexachlorofluorescein (HEX), TET, 6-Carboxy-4′,5′-dichloro-2′,7′-dimethodyfluorescein (JOE), N,N,N′,N′-Tetramethyl-6-carboxyrhodamine (TAMRA), 6-Carboxy-X-rhodamine (ROX), 5-Carboxyrhodamine-6G (R6G5), 6-carboxyrhodamine-6G (RG6), Rhodamine, Rhodamine Green, Rhodamine Red, Rhodamine 110, BODIPY dyes, such as BODIPY TMR, Oregon Green, Coumarines such as Umbelliferone, Benzimides, such as Hoechst 33258; Phenanthridines, such as Texas Red, Yakima Yellow, Alexa Fluor, PET, Ethidiumbromide, Acridinium dyes, Carbazol dyes, Phenoxazine dyes, Porphyrine dyes, Polymethin dyes, and the like.

In the context of the present invention, chemiluminescence based assays comprise the use of dyes, based on the physical principles described for chemiluminescent materials in Kirk-Othmer, Encyclopedia of chemical technology, 4^(th) ed., executive editor, J. I. Kroschwitz; editor, M Howe-Grant, John Wiley & Sons, 1993, vol. 15, p. 518-562, incorporated herein by reference, including citations on pages 551-562. Preferred chemiluminescent dyes are acridiniumesters. Chromogranin A may for example be detected using fully automated sandwich immunoassay systems on the B.R.A.H.M.S KRYPTOR compact PLUS instrument (Thermo Scientific B.R.A.H.M.S GmbH, Hennigsdorf/Berlin, Germany). This random access analyzer employs the sensitive Time Resolved Amplified Cryptate Emmission (TRACE) technology, based on a non-radioactive-transfer between two fluorophores.

In specific embodiments of the invention one of the antibodies (e.g. the first antibody) is labeled and the other antibody (e.g. the second antibody) is bound to a solid phase or can be bound selectively to a solid phase. However, as mentioned above, it is preferred in the context of methods of the invention that the first and the second antibody are present dispersed in a liquid reaction mixture, and wherein a first labelling component which is part of a labelling system based on fluorescence or chemiluminescence extinction or amplification is bound to the first antibody, and a second labelling component of said labelling system is bound to the second antibody so that, after binding of both antibodies to Chromogranin A (or fragment(s) thereof), a measurable signal which permits detection of the resulting sandwich complexes in the measuring solution is generated.

As mentioned herein, an “assay” or “diagnostic assay” can be of any type applied in the field of diagnostics. Such an assay may be based on the binding of an analyte to be detected to one or more capture probes with a certain affinity. Concerning the interaction between antibodies and target molecules or molecules of interest, the affinity constant is preferably greater than 10⁸ M⁻¹.

The immunoassay method of the present invention may be used in the context of diagnostic and/or prognostic methods in which the presence and/or absence or the level of Chromogranin A (or fragment(s) thereof) is detected in a sample from a subject to be diagnosed. Chromogranin A has been implicated with a number of diseases and conditions including carcinoid tumors, neuroendrocrine tumors, prostate cancer, bladder cancer, gastritis, pulmonary disease, myocardial infarction, hypertension, heart failure, pulmonary diseases, thrombolysis, obesity and diabetes. Hence, the immunoassay of the present invention may be used in the diagnosis of a disease or condition selected from the group of cancer (including carcinoid tumors, neuroendocrine tumors, prostate cancer and bladder cancer), gastritis, pulmonary disease, myocardial infarction, hypertension, heart failure, pulmonary diseases, thrombolysis, obesity and diabetes.

The “sensitivity” of an assay relates to the proportion of actual positives which are correctly identified as such, i.e. the ability to identify positive results (true positives positive results/number of positives). Hence, the lower the concentrations of the analyte that can be detected with an assay, the more sensitive is the assay. The “specificity” of an assay relates to the proportion of negatives which are correctly identified as such, i.e. the ability to identify negative results (true negatives/negative results). For an antibody the “specificity” is defined as the ability of an individual antigen binding site to react with only one antigenic epitope. The binding behaviour of an antibody can also be characterized in terms of its “affinity” and its “avidity”. The “affinity” of an antibody is a measure for the strength of the reaction between a single antigenic epitope and a single antigen binding site. The “avidity” of an antibody is a measure for the overall strength of binding between an antigen with many epitopes and multivalent antibodies.

The sensitivity and specificity of a diagnostic and/or prognostic test depends on more than just the analytical “quality” of the test, they also depend on the definition of what constitutes an abnormal result. In practice, Receiver Operating Characteristic curves (ROC curves), are typically calculated by plotting the value of a variable versus its relative frequency in “normal” (i.e. apparently healthy individuals not having a prenatal discorder or condition) and “disease” populations. For any particular marker, a distribution of marker levels for subjects with and without a disease will likely overlap. Under such conditions, a test does not absolutely distinguish normal from disease with 100% accuracy, and the area of overlap indicates where the test cannot distinguish normal from disease. A threshold is selected, below which the test is considered to be abnormal and above which the test is considered to be normal. The area under the ROC curve is a measure of the probability that the perceived measurement will allow correct identification of a condition. ROC curves can be used even when test results do not necessarily give an accurate number. As long as one can rank results, one can create a ROC curve. For example, results of a test on “disease” samples might be ranked according to degree (e.g. 1=low, 2=normal, and 3=high). This ranking can be correlated to results in the “normal” population, and a ROC curve created. These methods are well known in the art. See, e.g., Hanley et al. 1982. Radiology 143: 29-36. Preferably, a threshold is selected to provide a ROC curve area of greater than about 0.5, more preferably greater than about 0.7, still more preferably greater than about 0.8, even more preferably greater than about 0.85, and most preferably greater than about 0.9. The term “about” in this context refers to +/−5% of a given measurement.

The horizontal axis of the ROC curve represents (1-specificity), which increases with the rate of false positives. The vertical axis of the curve represents sensitivity, which increases with the rate of true positives. Thus, for a particular cut-off selected, the value of (1-specificity) may be determined, and a corresponding sensitivity may be obtained. The area under the ROC curve is a measure of the probability that the measured marker level will allow correct identification of a disease or condition. Thus, the area under the ROC curve can be used to determine the effectiveness of the test.

In other embodiments, a positive likelihood ratio, negative likelihood ratio, odds ratio, or hazard ratio is used as a measure of a test's ability to predict risk or diagnose a disorder or condition (“diseased group”). In the case of a positive likelihood ratio, a value of 1 indicates that a positive result is equally likely among subjects in both the “diseased” and “control” groups; a value greater than 1 indicates that a positive result is more likely in the diseased group; and a value less than 1 indicates that a positive result is more likely in the control group. In the case of a negative likelihood ratio, a value of 1 indicates that a negative result is equally likely among subjects in both the “diseased” and “control” groups; a value greater than 1 indicates that a negative result is more likely in the test group; and a value less than 1 indicates that a negative result is more likely in the control group.

In the case of an odds ratio, a value of 1 indicates that a positive result is equally likely among subjects in both the “diseased” and “control” groups; a value greater than 1 indicates that a positive result is more likely in the diseased group; and a value less than 1 indicates that a positive result is more likely in the control group.

In the case of a hazard ratio, a value of 1 indicates that the relative risk of an endpoint (e.g., death) is equal in both the “diseased” and “control” groups; a value greater than 1 indicates that the risk is greater in the diseased group; and a value less than 1 indicates that the risk is greater in the control group.

The skilled artisan will understand that associating a diagnostic or prognostic indicator, with a diagnosis or with a prognostic risk of a future clinical outcome is a statistical analysis. For example, a marker level of lower than X may signal that a patient is more likely to suffer from an adverse outcome than patients with a level more than or equal to X, as determined by a level of statistical significance. Additionally, a change in marker concentration from baseline levels may be reflective of patient prognosis, and the degree of change in marker level may be related to the severity of adverse events. Statistical significance is often determined by comparing two or more populations, and determining a confidence interval and/or a p value. See, e.g., Dowdy and Wearden, Statistics for Research, John Wiley & Sons, New York, 1983. Preferred confidence intervals of the invention are 90%, 95%, 97.5%, 98%, 99%, 99.5%, 99.9% and 99.99%, while preferred p values are 0.1, 0.05, 0.025, 0.02, 0.01, 0.005, 0.001, and 0.0001.

The invention further relates to a kit for the detection of Chromogranin A comprising

-   -   (i) a first antibody or antigen-binding fragment or derivative         thereof which is specific for Chromogranin A or a fragment         thereof; and     -   (ii) a second antibody or antigen-binding fragment or derivative         thereof which is specific for Chromogranin A or a fragment         thereof.

The first and second antibodies of the kit are preferably specific for the same Chromogranin A fragment or fragments.

For example, (i) the first antibody or antigen-binding fragment or derivative thereof is specific for an epitope comprised within the sequence of SEQ ID NO:1; and/or (ii) the second antibody or antigen-binding fragment or derivative thereof is specific for an epitope comprised within the sequence of SEQ ID NO:1. Preferably, the first antibody of the kit is a monoclonal anti-Chromogranin A antibody produced by hybridoma cell line 537/H2 deposited as DSM ACC3231 and/or the second antibody is a monoclonal anti-Chromogranin A antibody produced by hybridoma cell line 541/E2 deposited as DSM ACC3232.

The present invention also provides a hybridoma cell line selected from cell line 537/H2 deposited as DSM ACC3231 and cell line 541/E2 deposited as DSM ACC3232.

The invention e.g. further relates to the use of a kit according to the present invention in a sandwich immunoassay format for the detection and/or quantification of Chromogranin A or a fragment thereof in a biological sample from a bodily fluid. Such a fragment in one embodiment at least comprises a sequence spanning the two epitopes against which the two antibodies are directed, e.g. the kit can be used for the detection and/or quantification of Chromogranin A.

The term “sample” is preferably a biological sample. “Sample” as used herein may, e.g., refer to a sample of bodily fluid or tissue obtained for the purpose of diagnosis, prognosis, or evaluation of a subject of interest, such as a patient.

A “patient” or “subject” for the purposes of the present invention includes both humans and other animals, particularly mammals, and other organisms. Thus, the methods are applicable to both human diagnostics and veterinary applications. In a preferred embodiment the patient is a mammal, and in the most preferred embodiment the patient or subject is a human. Preferably herein, the sample is a sample of a bodily fluid or a tissue of the subject. A bodily fluid sample is preferred. Preferred test samples include blood, serum, plasma, cerebrospinal fluid, urine, saliva, sputum, and pleural effusions. In addition, one of skill in the art would realize that some test samples would be more readily analyzed following a fractionation or purification procedure, for example, separation of whole blood into serum or plasma components.

Thus, in a preferred embodiment of the invention the sample is selected from the group comprising a blood sample, a serum sample, a plasma sample, a cerebrospinal fluid sample, a saliva sample and a urine sample or an extract of any of the aforementioned samples. Preferably, the sample is a blood sample, more preferably a serum sample or a plasma sample. Serum samples are the most preferred samples in the context of the present invention.

“Plasma” in the context of the present invention is the virtually cell-free supernatant of blood containing anticoagulant obtained after centrifugation. Exemplary anticoagulants include calcium ion binding compounds such as EDTA or citrate and thrombin inhibitors such as heparinates or hirudin. Cell-free plasma can be obtained by centrifugation of the anticoagulated blood (e.g. citrated, EDTA or heparinized blood) for at least 15 minutes at 2000 to 3000 g.

“Serum” is the liquid fraction of whole blood that is collected after the blood is allowed to clot. When coagulated blood (clotted blood) is centrifuged serum can be obtained as supernatant. It does not contain fibrinogen, although some clotting factors remain.

Where appropriate, the sample may need to be homogenized, or extracted with a solvent prior to use in the present invention in order to obtain a liquid sample. A liquid sample hereby may be a solution or suspension. Liquid samples may be subjected to one or more pre-treatments prior to use in the present invention. Such pre-treatments include, but are not limited to dilution, filtration, centrifugation, concentration, sedimentation, precipitation, dialysis. Pre-treatments may also include the addition of chemical or biochemical substances to the solution, such as acids, bases, buffers, salts, solvents, reactive dyes, detergents, emulsifiers, chelators.

The method of the invention further relates to the determination of the level of Chromogranin A (or fragment(s) thereof) in a sample for diagnosis or prognosis or risk assessment or screening or therapy control or post-operative control for medical conditions.

The immunoassay, antibody or kit of the invention may therefore be used for the diagnosis, prognosis, risk assessment, risk stratification, therapy control and/or for post-operative control of a disorder or medical condition in a subject.

In the context of the present invention, the immunoassay, antibody or kit of the invention may therefore be used for therapy control and post-operative control of a disorder, wherein the disorder may be different types of cancer.

As mentioned herein above, in the context of the present invention, the disorder or medical condition in the subject may preferably be selected from cancer (including carcinoid tumors, neuroendocrine tumors, prostate cancer and bladder cancer), gastritis, pulmonary disease, myocardial infarction, hypertension, heart failure, pulmonary diseases, thrombolysis, obesity and diabetes.

In the context of the present invention, the disorder or medical condition in the subject is preferably selected from neuroendocrine tumours (NETs) including pheochromocytomas, pancreatic NETs, gastrointestinal NETs, neuroblastomas, medullary thyroid carcinomas, small cell lung cancer, multiple endocrine neoplasia 1 and multiple endocrine neoplasia 2 syndromes, prostate cancer, cardiovascular diseases, conditions related to infections and sepsis.

The term “biomarker” (biological marker) relates to measurable and quantifiable biological parameters (e.g., specific enzyme concentration, specific hormone concentration, specific gene phenotype distribution in a population, presence of biological substances) which serve as indices for health- and physiology-related assessments, such as disease risk, psychiatric disorders, environmental exposure and its effects, disease diagnosis, metabolic processes, substance abuse, pregnancy, cell line development, epidemiologic studies, etc. Furthermore, a biomarker is defined as a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. A biomarker may be measured on a biosample (as a blood, urine, or tissue test), it may be a recording obtained from a person (blood pressure, ECG, or Holter), or it may be an imaging test (Uteroplacental Doppler ultrasound, or nuchal translucency (Conde-Agudelo et al. 2004. Obstet Gynecol 104: 1367-1391; Bindra et al. 2002. Ultrasound Obstet Gynecol 20: 219-225)). Biomarkers can indicate a variety of health or disease characteristics, including the level or type of exposure to an environmental factor, genetic susceptibility, genetic responses to exposures, biomarkers of subclinical or clinical disease, or indicators of response to therapy. Thus, a simplistic way to think of biomarkers is as indicators of disease trait (risk factor or risk biomarker), disease state (preclinical or clinical), or disease rate (progression). Accordingly, biomarkers can be classified as antecedent biomarkers (identifying the risk of developing an illness), screening biomarkers (screening for subclinical disease), diagnostic biomarkers (recognizing overt disease), staging biomarkers (categorizing disease severity), or prognostic biomarkers (predicting future disease course, including recurrence and response to therapy, and monitoring efficacy of therapy). Biomarkers may also serve as surrogate end points. A surrogate end point is one that can be used as an outcome in clinical trials to evaluate safety and effectiveness of therapies in lieu of measurement of the true outcome of interest. The underlying principle is that alterations in the surrogate end point track closely with changes in the outcome of interest. Surrogate end points have the advantage that they may be gathered in a shorter time frame and with less expense than end points such as morbidity and mortality, which require large clinical trials for evaluation. Additional values of surrogate end points include the fact that they are closer to the exposure/intervention of interest and may be easier to relate causally than more distant clinical events. An important disadvantage of surrogate end points is that if clinical outcome of interest is influenced by numerous factors (in addition to the surrogate end point), residual confounding may reduce the validity of the surrogate end point. It has been suggested that the validity of a surrogate end point is greater if it can explain at least 50% of the effect of an exposure or intervention on the outcome of interest. For instance, a biomarker may be a protein, peptide or a nucleic acid molecule.

Herein “Chromogranin A” refers to human Chromogranin A. The amino acid sequence of human Chromogranin A is given in SEQ ID NO:1. The Chromogranin A polypeptides or derivatives according to the invention may also have posttranslational modifications such as glycolization, lip(o)idization, or derivatization.

“Diagnosis” in the context of the present invention relates to the recognition and (early) detection of a disease or clinical condition in a subject and may also comprise differential diagnosis. Also the assessment of the severity of a disease or clinical condition may in certain embodiments be encompassed by the term “diagnosis”.

“Prognosis” relates to the prediction of an outcome or a specific risk for a subject suffering from a particular disease or clinical condition. This may include an estimation of the chance of recovery or the chance of an adverse outcome for said subject.

In the present invention, the term “risk assessment” or “risk stratification” relates to the grouping of subjects into different risk groups according to their further prognosis. Risk stratification also relates to stratification for applying preventive and/or therapeutic measures.

The term “therapy control” in the context of the present invention refers to the monitoring and/or adjustment of a therapeutic treatment of said patient.

The term “post-operative control” in the context of the present invention refers to the monitoring of said patient following a surgical procedure of said patient.

The term “screening” in the context of the present invention refers to a process of surveying a population, using a specific marker or markers and defined screening cut-off levels, to identify the individuals in the population at higher risk for a particular disorder. Screening is applicable to a population; diagnosis is applied at the individual patient level.

The following examples and figures are used for a more detailed explanation of the invention, but do not limit the invention to said examples and figures.

All patent and non-patent references cited herein are hereby incorporated by reference in their entirety.

Sequences:

Sequence 1 (SEQ ID NO:1): Human Chromogranin A (CGA) without signal peptide (UniProt Accession no. P10645); antigenic epitopes are underlined:

1          11         21         31 LPVNSPMNKG DTEVMKCIVE VISDTLSKPS PMPVSQECFE 41         51         61         71 TLRGDERILS ILRHQNLLKE LQDLALQGAK ERAHQQKKHS 81         91         101        111 GFEDELSEVL ENQSSQAELK EAVEEPSSKD VMEKREDSKE 121        131        141        151 AEKSGEATDG ARPQALPEPM QESKAEGNNQ APGEEEEEEE 161        171        181        191 EATNTHPPAS LPSQKYPGPQ AEGDSEGLSQ GLVDREKGLS 201        211        221        231 AEPGWQAKRE EEEEEEEEAE AGEEAVPEEE GPTVVLNPHP 241        251        261        271 SLGYKEIRKG ESRSEALAVD GAGKPGAEEA QDPEGKGEQE 281        291        301        311 HSQQKEEEEE MAVVPQGLFR GGKSGELEQE EERLSKEWED 321        331        341        351 SKRWSKMDQL AKELTAEKRL EGQEEEEDNR DSSMKLSFRA 361        371        381        391 RAYGFRGPGP QLRRGWRPSS REDSLEAGLP LQVRGYPEEK 401        411        421        431 KEEEGSANRR PEDQELESLS AIEAELEKVA HQLQALRRG

Sequence 2 (SEQ ID NO:2): Epitope 1 of human Chromogranin A (CGA) (corresponding to residues 124-144 of SEQ ID NO: 1):

1          11         21 SGEATDGARP QALPEPMQES K

Sequence 3 (SEQ ID NO:3): Epitope 2 of human Chromogranin A (CGA) (corresponding to residues 280-301 of SEQ ID NO:1):

1          11         21 EHSQQKEEEE EMAVVPQGLF RG

Sequence 4 (SEQ ID NO:4): Antigenic peptide fragment of human Chromogranin A (CGA) (corresponding to residues 124-144 of SEQ ID NO:1 plus additional cystein at the N-terminal):

1          11         21 CSGEATDGAR PQALPEPMQE SK

Sequence 5 (SEQ ID NO:5): Antigenic peptide fragment of human Chromogranin A (CGA) (corresponding to residues 280-301 of SEQ ID NO:1 plus additional cystein at the N-terminal):

1          11         21 CEHSQQKEEE EEMAVVPQGL FRG

EXAMPLES Example 1: Generation of Antibodies

Development of Monoclonal Antibodies

Immunogens were prepared as follows: CSGEATDGARPQALPEPMQESK (SEQ ID NO:4) peptide corresponding to the amino-acids region 124-144 of Chromogranin A molecule with an additional cystein at its N-terminal was covalently cross-linked with the carrier BSA. CEHSQQKEEEEEMAVVPQGLFRG (SEQ ID NO:5) peptide corresponding to the amino-acids region 280-301 of Chromogranin A molecule with an additional cystein at its N-terminal was covalently cross-linked with the carrier BSA.

Monoclonal antibodies against the Chromogranin A 124-144 and 280-301 peptides were generated by standard procedures (Harlow E, Lane D. Antibodies—A Laboratory Manual. Cold Spring Harbor: Cold Spring Harbor Laboratory, 1988; Lane 1985. Journal of Immunology Methods 81: 223-228).

8-week-old female Balb/c mice were respectively immunized with by intra-peritoneal injections with 100 μg of 124-144 or 280-301 peptides diluted in complete Freund's adjuvant. Next injections were done using incomplete Freund's adjuvant at a 50 μg dose and at different time intervals during 61 days.

Prior fusion, the presence of the desired antibody was detected in the sera of the recipients using ELISA with 124-144 or 280-301 immobilized peptide. Then the clones 537/H2 and 541/E2 were screened by ELISA with immobilized rec. CGA (recombinant Chromogranin A was prepared by the French National of Scientific Research, “Plate-forme de Production de Protéines Recombinantes” CRBM UMR 5237 CNRS, Montpellier).

For the isotype characterization, the Mouse Monoclonal Antibody Isotyping Kit (Roche) was used.

The antibodies were purified by protein A Fast Flow affinity chromatography (GE Healthcare Life Sciences) according to the manufacturer's instructions.

Labelling of Antibodies

In the final assay, the antibody 537/H2 was coupled to europium cryptate (CisBio Bioassays, Marcoule, France) and the antibody 541/E2 was coupled to Alexa Fluor 647® (Life Technologies, now part of Thermo Fisher Scientific). The coupling reactions were performed according to the manufacturer's protocols.

Example 2: Development of a Chromogranin A Assay Using 124-144/280-301 Amino Acid Region Targeted Antibodies

A homogenous sandwich fluoroimmunoassay using Time Resolved Amplified Cryptate Emission (TRACE) technology (Mathis, 1993. Clin Chem 39(9): 1953-9) was developed for the detection of a stable fragment of Chromogranin A.

The stock Cryptate-537/H2 conjugated antibody and Alexa Fluor®-541/E2 conjugate antibody were diluted at 0.265 μg/ml and 2.94 μg/ml with assay buffer (100 mM phosphate pH 7, 422 mM KF, 0.1% bovine serum albumin, 0.15 mg/ml mouse Ig and 0.07 mg/ml bovine Ig) respectively, prior to use.

The recombinant Chromogranin A was diluted in horse serum to give Chromogranin A standards. The immunoassay was performed by incubating 14 μl of sample/standard, 68 μl of Alexa Fluor®-541/E2 conjugate antibody solution and 68 μl of Cryptate-537/H2 conjugated antibody solution at 37° C. on B.R.A.H.M.S KRYPTOR instrument (Thermo Fisher Scientific B.R.A.H.M.S GmbH, Hennigsdorf/Berlin, Germany), according to the manufacturer's instructions. The reaction time of the assay was 29 min. The specific fluorescence (RFU) was measured by simultaneous dual wavelength measurement at 665 and 620 nm using a B.R.A.H.M.S KRYPTOR instrument. Direct reading range was defined up to 3000 ng/ml and functional assay sensitivity estimated to be of 13.1 ng/ml.

Example 3: Stability Following of Chromogranin A in Serum Samples Pools Using the CgA II Assay

Three serum samples pools that had been frozen at ≦−16° C. just after collection were used for the study.

One pool was made from healthy individual serum samples (Pool 1) and the other two from pathological serum samples (pools 2 and 3).

Measurement time points were: after 1, 2 and 3 days at 2-8° C.; after 1, 2 and 3 days at 18-25° C.; after 1, 2 and 3 freeze/thaw cycles.

The measurements were done on a KRYPTOR instrument with the reagents and under conditions described above.

The criteria stated for considering stability of sample as acceptable is a loss ≦10% under the different conditions.

Results obtained (Table 1) show that the (537/H2-Cryptate; 541/E2-Alexa Fluor®) KRYPTOR assay is not sensitive to up to 3 freeze/thaw cycles, one day at 2-8° C. or at 18-25° C. The stability of the 2 pathological pools is better than the stability observed for the healthy-donors pool, as only a limited decrease of concentration is observed after 3 days at 2-8° C. or 18-25° C. (≦11%).

TABLE 1 Stability following of 3 serum samples pools using 537/H2-Cryptate; 541/E2-Alexa Fluor ® on KRYPTOR POOL 1 POOL 2 POOL 3 Conc. Conc. Conc. Conditions (ng/ml) / Ref. (ng/ml) / Ref. (ng/ml) / Ref Reference 85.5 — 880 — 2153 — 3 days 2-8° C. 65.7 −23% 786 −11% 1981 −8% 2 days 2-8° C. 62.9 −26% 797  −9% 2011 −7% 1 day 2-8° C. 79.8  −7% 825  −6% 2096 −3% 3 days 18-25° C. 69.9 −18% 789 −10% 1976 −8% 2 days 18-25° C. 71.2 −17% 798  −8% 2047 −5% 1 days 18-25° C. 78.5  −8% 816  −7% 2070 −4% 3 freeze/thaw cycles 82.8  −3% 851  −3% 2131 −1% 2 freeze/thaw cycles 90.4  6% 862  −2% 2137 −1% 1 freeze/thaw cycle 85.4  0% 875  −1% 2153  0%

Example 4: Calibration Curve

FIG. 1 shows the dose response curve for the (537/H2-Cryptate; 541/E2-Alexa Fluor647®) KRYPTOR assay using Time Resolved Amplified Cryptate Emission (TRACE) technology. Based on the calibration curve, the direct reading range for (537/H2-Cryptate; 541/E2-Alexa Fluor647®) KRYPTOR assay is defined up to 3000 ng/ml.

Example 5: Precision Profile and Sensitivity

91 samples (24 from healthy donors and 67 pathological samples) were measured in parallel using the 537/H2 and 541/E2 antibodies in the conditions described above and the prior art KRYPTOR Chromogranin A assay (Thermo Fisher Scientific B.R.A.H.M.S GmbH, Hennigsdorf, Germany). Measurements were performed in duplicates and the coefficient of variation of each duplicate was plotted against Chromogranin A concentration on the same graph. The precision profile are equivalent for both assays. Functional assay sensitivity claimed for the KRYPTOR Chromogranin A assay is 9.04 ng/ml; with (537/H2-Cryptate; 541/E2-Alexa Fluor647®) KRYPTOR assay, the functional assay sensitivity estimated for a 10% CV is 13.1 ng/ml. 

1. An immunoassay method for detection of Chromogranin A or a fragment thereof comprising: a) contacting a sample suspected of comprising Chromogranin A with (i) a first antibody or an antigen-binding fragment or derivative thereof specific for Chromogranin A, wherein the first antibody or antigen-binding fragment or derivate thereof is specific for an epitope comprised in the sequence spanning amino acid residues 124 to 144 according to SEQ ID NO:1 and (ii) a second antibody or an antigen-binding fragment or derivative thereof specific for Chromogranin A, under conditions allowing for formation of a ternary complex between Chromogranin A and the two antibodies or antigen-binding fragments or derivates thereof, and b) detecting the binding of the two antibodies or antigen-binding fragments or derivates thereof to Chromogranin A.
 2. The immunoassay method according to claim 1, wherein the second antibody or antigen-binding fragment or derivate thereof is specific for an epitope comprised in the sequence spanning amino acid residues 280 to 301 according to SEQ ID NO:1.
 3. The immunoassay method according to claim 1, wherein the first antibody is produced by the hybridoma cell line 537/H2 deposited as DSM ACC3231.
 4. The immunoassay method according to claim 1, wherein the second antibody is produced by the hybridoma cell line 541/E2 deposited as DSM ACC3232.
 5. The immunoassay method according to claim 1, wherein the sample is derived from a bodily fluid or tissue of a subject optionally bodily fluid selected from blood, serum, plasma and urine.
 6. The immunoassay method according to claim 1, wherein the assay is performed in homogeneous phase or in heterogeneous phase.
 7. The immunoassay method according to claim 1, wherein one of the antibodies is labeled and the other antibody is bound to a solid phase or can be bound selectively to a solid phase.
 8. The immunoassay method according to claim 1, wherein the first and the second antibody are present dispersed in a liquid reaction mixture, and wherein a first labelling component which is part of a labelling system based on fluorescence or chemiluminescence extinction or amplification is bound to the first antibody, and a second labelling component of said labelling system is bound to the second antibody so that, after binding of both antibodies to the Chromogranin A to be detected, a measurable signal which permits detection of the resulting sandwich complexes in the measuring solution is generated.
 9. The immunoassay method according to claim 8, wherein the labelling system comprises rare earth cryptates or chelates in combination with a fluorescent or chemiluminescent dye, optionally cyanine type.
 10. A monoclonal antibody which is produced by a hybridoma cell line selected from cell line 537/H2 deposited as DSM ACC3231 and cell line 541/E2 deposited as DSM ACC3232.
 11. A kit for the detection of Chromogranin A comprising (i) a first antibody or antigen-binding fragment or derivative thereof which is specific for Chromogranin A wherein the first antibody or antigen-binding fragment or derivative thereof is specific for an epitope comprised within the sequence spanning amino acids 124 to 144 of SEQ ID NO:1; and (ii) a second antibody or antigen-binding fragment or derivative thereof which is specific for Chromogranin A.
 12. The kit according to claim 11, wherein the second antibody or antigen-binding fragment or derivative thereof is specific for an epitope comprised within the sequence spanning amino acids 280 to 301 of SEQ ID NO:1 of Chromogranin A.
 13. The kit according to claim 12, wherein (i) the first antibody is selected from cell line 537/H2 deposited as DSM ACC3231, (ii) the second antibody selected from cell line 541/E2 deposited as DSM ACC3232.
 14. The immunoassay method according to claim 1, for the diagnosis, prognosis, risk assessment, risk stratification, therapy control and/or post-operative control of a disorder or medical condition in a subject.
 15. The method according to claim 14, wherein the disorder or medical condition is selected from the group consisting of cancer, gastritis, pulmonary disease, myocardial infarction, hypertension, heart failure, pulmonary diseases, thrombolysis, obesity and diabetes. 